Investigation On The Inhibitors And Fatty Acid Decomposers Limiting Seed Oil Accumulation In Rapeseed(Brassica Napus L.)

Rapeseed is one of the most important oil crops of the world ranking the third after soybean(Glycine max)and palm(Trachycarpus fortunei).It is the oil crop most widely grown in China.In comparison with oil yield of some rapeseed growing countries such as Germany and Canada,the oil yield level of rapeseed in China is much lower.To secure national edible oil supply,it is critically important to increase oil yield level in China and shorten the distance between China and other countries in respect of seed oil content(SOC).There were many previous efforts to elevate rapeseed SOC,such as to promote the activties of enzymes on the fatty acid(FA)biosynthesis pathway,block substrate competetions,and controll the stimili of environmental factors on regualtors of lipid biosynthesis.However,there is a paucity of knowledge relavant to FA reduction in maturing seeds,as well as about the inhibitors that eventually limit the efficient synthesis of seed lipid.To satisfy the above concerns,a series of experiments were designed and conduced to investigate(1)the genotyic differences of FA reduction in maturing seeds and the respective transcriptomes;(2)the effect of daily temperature period(DTP)on SOC of different genotypes;(3)the association of allelic variation of BnaC.TT2.a,a inhibitor of SOC,with seed color,seed FA content and compositions.The main findings are summerized as the following.1.There were genotypic differences among Zhongyou-511,Zheyou-50,Jiu-Er-13Xi and B6-3 for the reduction of FA in maturing seeds.The FA in the maturing seed of Zhongyou-511 declined drastically with a rate of 16.8%.In contrast,the FAs in maturing seeds of other three genotypes increased contineously.Analysis of the transcriptomes of Zhongyou-511 seeds at 40-DAP and 16-DAP revealed that the drastic drop of Zheyou-511 SOC was accompanied by the upregulation of 13648 genes and downregulation of 15239 genes(significance at|log2(FoldChange)|>1,Q<0.005).KEGG(kyoto encyclopedia of genes and genomes)analysis indicates that the up regulated genes included those for crabonhydrates metabolism and FA?-oxidition.A list of major genes that led to the drop of SOC in Zhongyou-511 was proposed.2.DTP affacted SOC significantly in both high(Zheyou-50)or low(Jiu-Er-13Xi)genotypes.Large day and night temperature differtences(LDNTD)gave rise to higher SOC in both genotypes.Relative to SDNTD,LDNTD resulted in 13.74%and 18.9%higher SOCs in Zheyou-50 and Jiuer-13,respectively.Low temperature in night inhibited the expression of the genes on the glyoxylae metabolism pathway(GMP),and also affected gibbrellin(GA)signaling.The transcriptional levels of the genes relating to oilbody formation was quite different between day and night,snychronized with the expressional pattern of genes on GMP.Analysis of promoter sequences revealed that most of the GMP genes characterize with a conservative GAGA-similar motif,a cis-element which responds to high temperture.Deep mining of the transcriptome data reveals that the low night temperture of the LDNTD system repressed the expression of DELLA proteins,which was further confirmed by RT-qPCR experiments.A two-year and two-location field experiment verified that the spray of paclobutrazol,a decomposer of GA,resulted in signifcant increases of oil yield at the rates between 9-18%depending on year and location.3.Signifcant association between allelic variation of BnaC.TT2.a locus and seed color,FA content and FA composition in a collection of 83 rapeseed germplasm was detected.This population was constructed not only for analyzing the loci regualting SOCs,but also for other functional genes.Four SNPs on intron 1 of BnaC.TT2.a were associated with seed FA.In addition,an InDel at position 738 on exon 3 of BnaC.TT2.a indicated a change of protein function that was significantly associated with seed coat color,linoleic acid(C18:2),and total FA content.